The influence of age on the use of potential enrichment objects and synchronisation of behaviour of pigs

This experiment aimed to identify how a pig's age affected the extent and synchrony of use of different environmental enrichment materials, and how this use changed over time. Ten diverse novel objects were each presented to three replicate litters of 3 weeks of age (sucklers) and three replicate groups of three animals of 5 (weaners) weeks and 13 (growers) weeks of age. Video recordings were made of the pigs’ behaviour over a period of 5 days and subsequently analysed for activity, inactivity and object directed behaviour of three animals per group on days 1 and 5. The observed performance of any given behaviour, when at least one other member of the group was also performing that behaviour, was compared with the probability that such concurrence occurred by chance and these results were used to calculate the degree of synchronisation. Gender had no effect on the duration of object use or approach latency. Growers displayed a shorter latency to approach the objects initially compared to sucklers and weaners (mean seconds; 2153 versus 2660 versus 980 for sucklers, weaners and growers, respectively, S.E.D. 542, p = 0.007). Sucklers used the objects to a much lesser extent than either the weaners or growers (mean duration object interaction (s); 129 versus 1253 versus 1412 for sucklers, weaners and growers, respectively, S.E.D. 93, p < 0.001). Overall object use decreased between days 1 and 5 (mean duration object interaction (s); 1326 versus 536 for days 1 and 5, respectively, S.E.D. 76, p < 0.001). All of the age groups synchronised their behaviour to a much greater extent than expected by chance. The sucklers showed a higher degree of synchrony of activity (K; 0.890 versus 0.776 versus 0.682 for sucklers, weaners and growers respectively, S.E.D. 0.013, p < 0.001) and inactivity (K; 0.963 versus 0.905 versus 0.909 respectively, S.E.D. 0.007, p < 0.001), but lower degree of synchrony for object directed behaviour (K; 0.149 versus 0.375 versus 0.370 respectively, S.E.D. 0.025, p < 0.001), than the weaners and growers. The degree of synchronisation of object directed behaviour decreased over the 5-day period, irrespective of age (K; 0.382 versus 0.214 for days 1 and 5 respectively, S.E.D. 0.020, p < 0.001). Significant correlations (r = 0.678–0.879) were found between the degree of synchrony and extent of object interaction only for the sucklers. Since pigs showed behavioural synchronisation, object availability should be considered when providing desirable enrichment in order to avoid excessive competition in larger commercial groups.